Ultra-short wave transmitting system



@et l5, E935. F. H KRQGER ULTRA-SHORT WAVE THANSMITTING SYSTEM Filed May A17, 1932 3 Sheets-Sheet l INVENToR F H KnoeaR BY if@ SQQSQ Q @VSQQSQ Q @CL i5, 1935. H KRQGER ULTRA-SHORT WAVE TRANSMITTING SYSTEM 5 sheets4sheet 2 Filed May 17, 1952 @et l5, 1935. F, H. KROGER ULTRA-SHORT WAVE TRANSMITTING SYSTEM Filed May 17, 1952 3 Sheets-Sheet 3 EQ Ss NT S ATTORNEY NVENTOR F H KRO ER BY I ANW Patented Oct. 15, 1935 UNITED STATES PATENT OFFICE ULTRA-SHORT WAVE TRANSMITTING SYSTEM Ware Application May 17, 1932, Serial No. 611,769

Claims.

This invention relates to a method of and apparatus for relaying radio signals.

It is well known that electromagnetic waves at the lower wave lengths below ten meters have 5 characteristics which are quasi-optical in nature; that is, they have a very definite limited range of transmission which is comparable with the optical range or Visible distance. It has been found that the inter-position of objects in the path of transmission of such wave aects, to an extent at least, the ability of a station toreceive the radiated energy, and that the condition of the local topography is an important element of consideration in ultra-short wave communication. One arrangement heretofore suggested for transmitting ultra-short wave signals between points separated by a distance greater than the optical range has been to locate relay or repeater stations at frequent intervals along the line of transmission for amplifying and reradiating the signals. It has been proposed heretofore to provide these relay stations with two directive antenn, one for receiving the signal from the station nearest the transmitting end and the other for reradiating the signal to the next adjacent station nearest the receiving terminal.

In all prior art arrangements, however, the stations have been designed to operate on a single frequency, a mode of operation which introduces great difficulty in maintaining stability of the system. In order to maintain stability and prevent self-oscillation in such relay stations, the receiving and transmitting antennae of each repeater must be so located and must have such sharp directive characteristics that the energy reradiated from the transmitting antenna does not feed back into the receiving antenna. Since the ratio between the input and output levels of these two antennae may be of the order of several million to one, it is extremely diirlcult if not impossible to make such a system operate ina practical manner.

This difficulty, due to instability or self-oscillation of the amplifiers at the repeater stations, is obviated in the present invention by utilizing different frequencies on the two antennae. According to the present invention it is proposed to receive the signals at a repeater station Yon one frequency, change its frequency to another frequency which differs from the first frequency by a desired amount and then amplify and reradiate the new frequency.

A system designed in accordance with this invention is 'not limited in scope to the transmission of any one type of radio signal, but may be utilized to transmit telegraph signals, television, telephony or other suitableforms of modulation. When used for the transmission of television or telephone Vbroadcasting for the syndication of programs between points which are widely sep- 5 arated, the repeater stations of the present system are useful not only as relay stations, but may also be used as local broadcasting stations in rural districts where the economics of the situation do not otherwise warrant the erection of l0 television or telephone broadcasting stations. For example, a radio transmission linemight lbe used to send programs (television, telephone or both) from New York to Chicago. Such line would pass through rural areas. Due to the fact that the re- 15 peater stations are provided with highly directionalantennae, for reasons of efliciency in operation, these areas would otherwise be beyond the range of the ultra-short wave broadcasting stations at the terminals of the line due to the quasi- 20 optical nature of the electromagnetic waves used. If desired,it may be advisable to provide' at one or more repeater stations on the transmission line a non-directional (broadcasting) transmitter in addition. to the directional type. Accordingly, 25 whatever programs are passed over the line would be spread out at right angles to the transmission line as well `as in the direct line of transmission and would thus give service to a particular area.

One of the features of the present invention is 30 the automatic change-over equipment for substituting one transmitter for another in the event of failure of radiation. Likewise, two rectifiers with automatic change-over apparatus are provided at each station. 35

A Abetter understanding of the invention may be had by referring to the following description, accompanied by drawings wherein Figure 1 shows,'diagrammatically, aradio communication system -embodying the principles of 40 the present invention, and

Figure 2 illustrates, diagrammatically, one form of repeater station circuit which may be utilized in the present system.

Figures 3 and 4 are line or schematic diagrams 45 of the change-over equipment.

Referring in more detail to Figure 1, there are shown a transmitting station A and a receiving rstation C between which it is desired to transmit signals. ings by the direction of the arrows, station A is arranged Lto transmit signals and station C toY receive signals. Intermediate A `and C are a plurality of repeater stations R, R `and R".

These repeaters are each provided with two di- 55- As indicated in the draw- 50 Y rectional antenn, one of which is adapted to receive signals and is operative in the direction of the next adjacent transmitting station and the other of which is adapted to transmit sig- 5 nals in the direction of the next adjacent receiving station. Since the transmission range of the ultra-short waves depends upon the air line or visual distance, a factorv proportional to the height above the earths surface, it is proposed to locate all stations at points having as great height as possible, such as mountains, tall buildings, radio masts, etc.

The directional antennae may be of any suitable type and may or may not use reflectors. If, for example, the transmitter is designed to operate on frequencies above 300,000 kilocycles (below one meter), highly directive antennae of compact construction may be used. A transmitting antenna such as developed at present for frequencies above 300,000 kilocycles consists of a copper sheet about 6 feet wide by 6 feet long, on which are mounted insulators for supporting a system of half wave elements parallel to and one-quarter a wave length away from, the copper sheet. The sheet acts as a reflector. On a two way circuit, i. e. where transmission may be effected in two directions, these antennae should be mounted back to back at the top of the repeater station tower and the receiving antennee should be mounted alongside the transmitting antennae.

For lower frequencies, of the order of 60,000 kilocycles (5 meters), other more extensive forms of directive antennae would be used, as for eX- ample, a type such as is disclosed by P. S. Carter in United States Patent No. 1,974,387, granted September 18, i934.

In Figure 1, frequencies of the order of 60,000 kilocycles are referred to for the purpose of illustration, but it is to be understood, of course, that the same principles apply to the use of higher or lower frequencies.

In Figure l, transmitting station A is designed to function on a frequency of 60,000 kilocycles. This signal is received at repeater R on the directive antenna r, amplified, converted to a new frequency of 59,000 kilocycles by beating with a local oscillator of 1,000 kilocycles and is then reradiated on directive antenna t at 59,000 kilocycles. At repeater R the 59,000 kilocycle signal is received on antenna r and is converted to a new frequency of 58,000 kilocycles, amplied and reradiated at 58,000 kilocycles on transmitting antenna t.

Likewise, at relay point R" the 58,000 kilocycle signal is received, converted to 60,000 kilocycles, amplified and reradiated. The 60,000 kilocycle signal has the same frequency as that originally transmitted at transmitter A. These same three frequencies maynow be used over again in the same sequence as many times as may be desired. Y Since the range of these ultr-a-short frequencies is limited to points slightly beyond the distance between the relay points it is impossible for the radiation of the 60,000 kilocycle signal from station C to reach back to repeater R which is capable of receiving 60,000 kilocycle energy. Thus, by the use of these three frequencies, all possibility of instability is entirely eliminated. Although theuse of three frequencies is preferable in this arrangement and is Vthought to be the most practical from an operating standpoint, it isto be understood that, if desired, a similar system utilizing only two frequencies with suitable directive antenna: may be employed.

At repeater station R' there is shown a'local broadcasting station B. The input of the transmitter B may be obtained, in any suitable manner, from the radio .transmission line signals, that is, the signals passing along the radio transmission line would be demodulated and used to control the broadcasting transmitter B located at the repeater station R. The frequency of transmission from this broadcasting transmitter may be any frequency other than the frequency used on the radio transmission line. Transmitter B is arranged to be an automatically operating broadcasting transmitter (as distinguished from a directional) and may be connected at any one or more of the repeater stations to serve rural areas with broadcasting service effectively. Of course, the power of the broadcasting transmitter may be adjusted'independently to whatever value it is desired to give adequate service.

In Figure 2 there is shown one manner of receiving a signal on one frequency and heterodyning this received signal with another frequency to obtain a third frequenly slightly different from the received frequency for reradiation purposes. The received signal fl received over the directive antenna will be amplied by the tuned radio frequency amplifier and impressed upon a suitable detector having a separate oscillator connected thereto. The output of this detector will'include the desired frequency f2 which, after aniplication and filtering, will be impressed upon a power ampliiier'for reradiation over the other directive antenna. It is to be understood that all the usual precautions which have been developed for short wave receiving equipment will be used, such as complete shielding, filtering of the leads, etc.

If desired, the last few power stages may be entirely separate from the radio frequency amplifier and, if necessary, placed in another screened room to reduce all possibility of feed-back in the equipment itself. 1

The transmission lines to the receiving and transmitting directive antenna of the circuit in Figure 2 are well separated Vand so positioned as to reduce the coupling between them to a minimum. The frequency dierence between the incoming and outgoing signals is sufficient to make it possible to readily separate the transmitted energy from the incoming energy at the receiver so that the system will tend to be entirely stable. Of course, if a quite large frequency diiference between the incoming and outgoing signals is used, the system tends to become inherently more stable and many of the precautions mentioned above may not be necessary.

In Figure 3 there vis shown, in a line diagram, suitable apparatus for automatically changing over from one rectier to another incase of failure of radiation in the transmitter. An emergency power supply is also included in case of failure in the power service. The operation of this circuit will now be described.

Assuming that theV outside powerl source designated in the drawings as a three phase alternating current220 volt supply is operative, relay 9 will be energized, in turn, closing the four switches interlocked on lever I3. The emergency power supply connecting' with switchll will be opened. In starting up the equipment, switch -I will be closed by the attendant causing voltage from the terminal 3 of battery li to flow through switch l, then over lead H0 to contact 5I of the plate relay 55. Current will also ow through reversing switch 83 to the biasing coil 65. Switch 83 may now be thrown to such a polarity that the pull of coil opposes the pull of the plate coil on the active rectifier. For example, if it is desired to use rectifier 2, which comprises 25 (high voltage rectifier #2), 2T (low voltage rectifier #2), and 53 (storage battery #2), switch 83 will be thrown to such a position that coil 65 opposes the closing of contacts 5| and 53 to the circuits of rectifier 2. The reason for this will be explained later.

Let it be assumed that it is desired to start up the apparatus, using rectifier 2 (elements 25, 2l, and 43) and leaving rectifier I (elements 45, 4l, and 49) as a standby. After switch 83 is thrown to the proper position, handle 61 should be pulled up against the magnetic pull from coil 35 in order to close contacts 5| and 53, the latter being operated by thimbles 'I9 and 8l mounted on the relay control handle. Current will then flow from contact 5| through lament contactor 36 back to the negative terminal 5 of battery 4. Current will also flow through contact 53 to high voltage relay coil 51, pulling up contacts 8l and 63, and connecting high voltage rectier 2 to the transmitter. When the lament contactor coil 36 is energized, contacts l5, 29, 3|, 33, and 35 are closed in an upward position. Contacts 2S, 3l, and 33 connect the three phase supply to rectier 2. Contact 35 connects storage battery 43 to the transmitter. Contact l5 connects the circuit from battery 4 through jack 2 and coil l'l to the negative side of battery 4.

Relay l'l is arranged for time delay in order Ato give the filaments of the rectier tubes time to warm up before contact lll closes. When contact I3 finally closes, battery current is passed through plate contactor coil 2| which, in turn, closes contact 23 applying the plate voltage to the rectifier.

During all this time it has been assumed that handle 5l of differential relay 55 was being pulled up by the attendant. However, as soon as the plate voltage is built up on rectifier 2 the rectifier plate voltage applied to coil 55 will oppose the pull of coil 55 and hold contacts 5| and 53 closed over the circuits associated with rectifier 2. The time within which this operation takes place is about two or three seconds, or whatever time may be required to heat up the filaments before contact i9 of the time delay relay closes.

Should it be desired to use rectifier l and its storage battery instead of rectifier 2, the starting up operation is exactly the same except that switch 83 will now be reversed and handle B'l pushed down instead of being pulled up. Once rectifier 2 has been put in operation in a manner heretofore described, it will continue to run until shut down by the attendant or, until for some unforeseen reason, rectifier 2 fails. Such a failure may be caused by a number of reasons, such as a filament burnout, a broken down condenser or a burned out resistance. It will be noted, however, that if the plate voltage of rectier 2 .should fail, then coil 55 of the differential relay would be rie-energized and coil 65 would function to pull down handle 6l.

in order to protect against momentary loss of voltage a dash pot 59 is utilized, having a piston "El which is arranged to force air out of vent 'I3 or l5 according to whether the piston is being pulled upward or downward. Under the present assumption of the operation of the apparatus. coil 55 is pulling the handle Bl downward causing the piston 'll to force air through vent '|5. If the plate voltage is not restoredwithin a short in'- terval of time, piston 'Hfwilldescend low enou'gh to cause collars 'l1 and 80 to open contacts 5| and 53 and close them to the lower contacts. As soon as contact 5l is broken the circuit through lilament contactor 35 will be opened, thus disconnecting the power supply from rectifier 2. When contact 5|. reaches the lower contact, coil 31 is energized and places the power supply on rectiiier l.

Rectifier 2 is arranged to be completely shut down while rectifier is started up with its proper sequence of events, that is, the lament circuits are energized before the plate voltage is put on. During this sequence of events, coil 65 is arranged to hold contacts 5| and 53 closed inthe downward position so that the change-over is entirely automatic. When the voltage of rectifier is built up, coil 55 is excited thereby, but the pull of coil 55 is now in the same direction as the pull on coil 65 and consequently nothing happens. It will be evident, therefore, that rectifier l is held in operation until the attendant is called to the station. After making repairs onthe recti- 1ier, the reversing switch 83 may be thrown to the opposite position so that coil 85 opposes the voltage from rectifier l in coil 55. If desired, the system may be left operating on rectifier l and,

' in case of failure, rectifier 2 may be put into service in a manner which is obvious from the foregoing. I

In the drawing of Figure 3 there is also shown one manner in which switching may be made to a spare rectier or, alternatively, to a spare rectier and transmitter, should radiation fail. Cable |35 is arranged to carry the power supp-ly from the rectifier system to transmitter |83, which is coupled to antenna lill. A rcoil |58 associated with bias rectifier 91 is also coupled to antenna lill. When no radiation takes place from antenna |8l battery 98 is arranged to bias tube Sl to cut-olf so that no plate current flows through resistance 93. For this condition, the grid of tube 89 is at the same potential as the filament of tube 89, which follows from the fact that there is no voltage drop across resistance 93. Consequently, plate current will flow in tube 85 through relay coil 81 holding contact 85 open against the pull of spring 86. On the other hand, if antenna ll is radiating, energy will be picked up by coil and will cause the grid of tube 9i' to swing positive, creating a fiow of plate current in tube 91 through resistance 93. The voltage drop across resistance 93 swings the'grid of tube 89 to zero and thereby causing the tongue of relay 8l to be drawn back by spring 85, closing contact 85.

From the foregoing, it will be apparent that as long as antenna l radiates in a normal manner, relay contact will be closed, but if the radiation fails, then relay contact 85 will be open. To protect against momentary interruption of the antenna current, condenser 9| has been placed in parallel with resistance 93 and the time con stant of this resistance-condenser circuit adjusted to a suitable value. If it is assumed, as mentioned above, that the operator has started up rectifier 2 after the system is in operation, the radiation from antenna l8l will close the contact 85 of relay B'l and the operator will then insert plug 88 into jack 2. kShould radiation now fail, the control circuit through contact I8 toI plate contactor 2| will be opened and the plate voltage removed from rectifier 2, thus causing rectifier l` to start up in a manner hereinabove described. From the foregoing, it will be obvious that rectier and rectier 2 may be associated with spare transmitters entirely independent of each other, in which case, a failure of radiation would cause the apparatus to be switched over to a spare transmitter.

In order to provide as great flexibility as possible in the operation of the circuit it may be preferable to utilize the arrangement shown in Figure 3 for insuring proper operation in the event only of a rectifier failure, and to use an arrangement that is only capable of switching the transmitters in case of radiation failure. In Figure 4 there is shown in line diagram an arrangement for effecting this purpose wherein there are shown two transmitters |33 and |35 having suitable contactors |4|, |43, and |45 for switching the power supply from one transmitter to the other. Interlocked with these contactors is a fourth contactor |39 which is arranged to energize coils |25 or |21, in turn, operating contacts |29 and 3|. These latter contacts switch the coupling coil |38 from one transmitter to the other.

Since the operation of the circuit shown in this figure is well known to anyone skilled in the art it will only be brieiiy described herein.

In starting up the arrangement, switch |5| is closed, thus energizing coil |49 from battery 53. Coil |49 connects all contactors in the upper position, as indicated in the drawing, therebyoperatively conditioning transmitter |33 for operation. The radiation in antenna ||3| is coupled through coil |55 to tube |09, producing an IR drop through resistance 3 which biases the grid of tube negative, causing the tongue of relay |2| to be pulled back byspring |24 and make Contact at |23. Switch |5| may now be opened since coil M9 is energized through contacts |23 and |41. In the event of failure of transmitter |33, radiation from antenna ||1| will cease and, should it fail long enough for the time constant circuit I3 and |55 to operate, the relay contact |23 will break the energizing coil |49 and throw all contacts |353, |4|, M3, and |45 to transmitter |35. In such case, contact 41 will also be opened so that, when antenna l is again radiating normally, the closing of contact |23 will have no effect on coil |49 and transmitter |35 will continue in operation until there is a manual switch-over to the other transmitter. It should be noted that the operation of relay |2| closed an alarm circuit over contact |54 which functions in an obvious manner to indicate an alarm at any desired locatien of the failure of the transmitter. A time delay unit |56 may be utilized, if desired, to prevent slight momentary failure frombeing indicated.

It is to be distinctly understood that this invention is not limited in application to the precise arrangements shown since it is apparent that they are susceptible of being modified to meet different conditions encountered in their use and it is, therefore, aimed to cover by claims all modifications within the spirit and scope of the present invention.

I claim:

1. An ultrashort wave radio relaying communication system comprising a first station, a 5

second station and a third station, each of said stations having a directive antenna pointed at its next adjacent station, apparatus for energizing said antennae to radiate two sets of power supply equipmentat each station for said apparatus, 10 only one set of said equipment being adapted to be operatively connected to said appartaus at a time, and means at each station responsive to a failure of radiation in its associated antenna for automatically changing-over from said operal5 tively connected set to the spare set.

2. An ultrashort Wave radio relaying communication system comprising a first station, a second station and a third station, each of said stations having Va directive antennapointed at its next adjacent station, two sets of power supply equipment at each station for enabling energization of said antennae, only one set of said equipment being adapted to be operatively connected to the antenna at a time, and means at each station responsive to failure of energization of its associated antenna for automatically changing-over from said operatively connected set to the spare set.

3. A relaying station for radio signal Waves comprising a receiving antenna and a transmitting antenna, meanst for amplifying the signals received over saidV receiving antenna and for applying them to said transmitting antenna for reradiation purposes, power supply equipment operatively in circuit with said last means, additional power supply equipment, and automatic change-over apparatus responsive to a' failureof radiation from said transmitting antenna for connecting said last power supply equipment to 40 said means.

fl. A relaying station for radio signal waves comprising a receiving antenna, a.` transmitting antenna, means for amplifying the signals received over the receiving antenna and for applying them to the transmitting antenna including two sets of transmitting apparatus for energizing said transmitting antenna, said transmitting antenna being adapted to be connected to only one of said sets at a time, and automatic change-over equipment responsive to a failure of radiation from said transmitting antenna for connecting said transmitting antenna to the spare transmitting apparatus.

5. In combination at a station in a communi- 5-5 cation system, a transmitting antenna, two sets of transmitting apparatus for energizing said antenna, said antenna being adapted to be connectedl to only one of said sets at a time, and automatic change-over equipment responsive to a failure of radiation from said transmitting antenna for connecting said antenna to the spare transmitting apparatus.

FRED H. KRJOGER. 

